A popular method for solving (REF ) is the iterative soft-thresholding algorithm (ISTA) [1]}:
\(x_{t+1} = \eta _{\lambda \tau }[x_t + \tau Q^{\hspace{-0.83328pt}\mathsf {T}}(y- Qx_t)], \qquad 0 \le t < T,\) 
